Well, a logo has to be unique and shomehow "organic" by essence ; self-contained by composition. Script fonts are more prone to defeat such requisites and far less forgiving than non script ones. If you know about calligraphy you also know that handwriting styles carry many more distinguishing subleties - not to say decisive discrepancies - than ready script fonts. Ready for what ? The Devil is in every smoothed detail of a script font. You don't need that much calligraphic skills to bring back the smile of God. But I agree that mastering calligraphy remains indeed a different kettle of fish.